The defendants face charges ranging from plotting against the establishment to violating security regulations, said the official IRNA news agency. Five of those on trial, including two women, were accused of "moharebeh," or defying God, a charge that could carry the death penalty, the semiofficial ISNA news agency reported.

The new prosecutions, coupled with the execution on Thursday of two men accused of involvement in anti-government groups, could mark an attempt by Iran's hard-line leaders to intimidate the opposition before a new round of street demonstrations expected in February.

Those who stood trial Saturday - including a follower of the Baha'i faith, an alleged communist and a student activist - were detained during anti-government demonstrations on Dec. 27. At least eight people were killed and hundreds more were arrested in those rallies, during which opposition activists and security forces clashed. The violence was the worst since authorities launched a harsh crackdown immediately after Iran's disputed presidential election in June.

The protesters have presented Iran's cleric-led establishment with its biggest challenge since the 1979 revolution despite a brutal crackdown that has left hundreds imprisoned.

IRNA quoted a prosecutor identified only by the last name of Farahani as saying in court that some of the defendants had confessed to spying, planning bomb attacks and damaging public and private property. He also said some of the defendants had sent videos of the clashes between protesters and Iranian police to "foreign hostile networks," IRNA reported.

Human rights groups have cautioned that such confessions are often made under duress in Iran.

The ISNA news agency quoted the student activist on trial, who was not named, as telling the court Saturday that he had given interviews to the foreign media about the protests since the "doors of the domestic media are closed to us."

Iranian authorities have banned many newspapers and news Web sites and detained many opposition journalists after the election.

The new trial comes amid a sweeping crackdown by Iran's clerical leaders against opposition activists in a bid to crush the challenge that has emerged to their rule in the wake of President Mahmoud Ahmadinejad's disputed re-election in June. The opposition says Ahmadinejad's victory was fraudulent.

Iran's hard-line government has quashed opposition rallies and tried more than 100 political activists in a mass trial that started in August, sentencing 11 people to death and more than 80 people to prison terms ranging from six months to 15 years.

On Thursday, authorities hanged two men who had been convicted of belonging to "counterrevolutionary and monarchist groups," plotting to overthrow "the Islamic establishment" and planning assassinations and bombings.

The men were arrested months before the election. But they were brought before judges in the same mass trial that started in August in an attempt by the leadership to show that the political opposition is in league with violent armed groups in a foreign-backed plot to overthrow the Islamic system.

Iran's main opposition leaders, Mir Hossein Mousavi and Mahdi Karroubi, denounced the executions and said they were likely meant to scare people into staying away from the planned Feb. 11 demonstrations, according to the pro-reform Web site Sahamnews.

After meeting Saturday, the two opposition leaders - both of whom ran against Ahmadinejad in June - urged people to turn out for next month's rallies.

The planned demonstrations are meant to coincide with anniversary of the 1979 Islamic Revolution. A display of opposition numbers on the most hallowed day in the Iranian political calendar would mark a stinging symbolic challenge to the clerical leadership.